Glow plugs, which are installed in internal combustion engines for igniting a fuel/air mixture, are preheated in the cold state until their temperature is high enough to be sufficient to ignite the fuel/air mixture. For this purpose, the glow plug has a heater which applies an excessively high heating voltage to the cold glow plug during a short time period of 1 to 2 seconds, so that the glow plug is overloaded at this point in time. After completion of this so-called push phase, the tip of the glow plug reaches a temperature of more than 1000° C., while the rest of the glow plug still has a temperature which is way below this temperature of 1000° C.
By activating the glow plug using an excessively high heating voltage, a temperature overshoot is produced on the glow plug. The temperature of the glow plug reached during the preheating phase represents an input variable for a control using which the temperature of the glow plug is set if same has reached a steady-state temperature characteristic. Since this input variable for the control is, however, ascertained during a transient reaction, this results in errors during the following control.